Linear motor with reduced cogging

ABSTRACT

A linear motor is provided including a magnet track including a plurality of permanent magnets, and a coil assembly including a plurality of laminations. The coil assembly defines a plurality of teeth having slots therebetween. The plurality of teeth include (1) two end teeth and (2) at least one non-end tooth arranged between the two end teeth. Each of the two end teeth defines an end profile including a first surface and a second surface. The first surface and the second surface are separated by a step which is substantially perpendicular to a plane defined by the plurality of magnets. The linear motor also includes a plurality of coils at least partially disposed in at least a portion of the slots defined by the plurality of teeth.

CROSS REFERENCE

This application claims the benefit of International Application No. PCT/US2006/062351 filed Dec. 20, 2006, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to linear motor systems, and more particularly, to linear motor systems with reduced cogging.

BACKGROUND OF THE INVENTION

Linear motors are well known in the art and used in many different industries. For example, linear motor systems are used in wire bonding machines to provide high speed linear motion along various axes. For example, in certain wire bonding machines, linear motors are used to provide precise high speed motion along an x-axis and a y-axis of the machine.

One problem well known in the field of linear motors is cogging. For example, cogging forces in linear iron-core synchronous/brushless DC motors is undesirable because it tends to act as a disturbance to the current/force loop of a servo system, thereby compromising servo system performance.

In linear motors including coil assemblies (e.g., laminated armatures including teeth configured to be wound with coils), one method of reducing cogging forces has been related to the design of the end teeth of the coil assembly. For example, U.S. Pat. No. 4,912,746 to Oishi reduces the unit volume of the teeth at the axial ends of the armature core by cutting out a section of the end teeth. In another example, U.S. Pat. No. 5,910,691 to Wavre provides end teeth 78, 80 having a first segment 84 adjacent a second sloped segment 86.

Therefore, while prior art attempts at reducing cogging effects in linear motors by specialized design of the end teeth of an armature are known, increased pressure for reduced cogging in linear motors continues in the industry.

Thus, it would be desirable to provide a linear motor system with reduced cogging.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a linear motor is provided. The linear motor includes a magnet track including a plurality of permanent magnets, and a coil assembly including a plurality of laminations. The coil assembly defines a plurality of teeth having slots therebetween. The plurality of teeth include (1) two end teeth and (2) at least one non-end tooth arranged between the two end teeth. Each of the two end teeth defines an end profile including a first surface and a second surface. The first surface and the second surface are separated by a step which is substantially perpendicular to a plane defined by the plurality of magnets. The linear motor also includes a plurality of coils at least partially disposed in at least a portion of the slots defined by the plurality of teeth.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:

FIG. 1 is a cross-sectional view of a linear motor in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view of a linear motor in accordance with another exemplary embodiment of the present invention;

FIG. 3A is a partial view of an end tooth of a coil assembly of a linear motor in accordance with an exemplary embodiment of the present invention;

FIG. 3B is a partial view of an end tooth of a coil assembly of a linear motor in accordance with another exemplary embodiment of the present invention;

FIG. 4A is a partial view of an end tooth of a coil assembly of a linear motor in accordance with yet another exemplary embodiment of the present invention;

FIG. 4B is a partial view of an end tooth of a coil assembly of a linear motor in accordance with yet another exemplary embodiment of the present invention;

FIG. 5A is a partial view of an end tooth of a coil assembly of a linear motor in accordance with yet another exemplary embodiment of the present invention; and

FIG. 5B is a partial view of an end tooth of a coil assembly of a linear motor in accordance with yet another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “magnet track” is intended to refer to any of a number of structures in a linear motor including a plurality of permanent magnets arranged to magnetically interact with a coil assembly of the linear motor such that a desired linear motion of at least one of the magnet track and the coil assembly is provided. As such, the magnet track is not intended to be limited, for example, to any particular arrangement or spacing of the permanent magnets, nor is the magnet track intended to be limited to any particular support structure for the permanent magnets.

FIG. 1 is a cross sectional view of linear motor 100. Linear motor 100 includes magnet track 101 and coil assembly 108. As is understood by those skilled in the art, certain components of linear motor 100 (e.g., electrical connections, etc.) have been omitted for simplicity.

Magnet track 101 includes support plate 102 (e.g., a steel plate) and a plurality of permanent magnets 104 disposed on support plate 102. For example, permanent magnets 104 may be glued or otherwise secured to support plate 102 at a predetermined spacing as is known to those skilled in the art. For purposes of describing certain exemplary features of the present invention, plane 106, which is substantially parallel to a top surface of permanent magnets 104, is shown in FIG. 1.

Coil assembly 108 includes a plurality of laminations 110 and a plurality of windings 112. Laminations 110 are stacked as is known to those skilled in the art, for example, to form an armature or the like. Exemplary materials for laminations 110 include silicon steel, low carbon steel, amongst many others. Stacked laminations 110 define base portion 110 a and a plurality of teeth 110 b extending from the base portion 110 a. It is understood by those skilled in the art that base portion 110 a may define certain features (e.g., alignment features, grooves, apertures, etc.) not shown in FIG. 1.

Slots 114 are defined between adjacent teeth 110 b; between end tooth 110 c and an adjacent tooth 110 b; and between end tooth 110 d and an adjacent end tooth 110 b. In the exemplary embodiment of the present invention illustrated in FIG. 1, flanged portions 110 e are defined at an end of each of teeth 110 b. Thus, in the exemplary embodiment of the present invention illustrated in FIG. 1, the width of slot 114 is smaller between flanged portions 110 e in contrast to the width of slot 114 along the remainder of the length of teeth 110 b extending back towards base portion 110 a.

Windings 112 (e.g., insulated windings) are provided in slots 114. For example, windings 112 may occupy each slot 114, or certain slots 114 may include windings 112 while other slots may remain empty. Further, a single slot 114 may be occupied by a single winding 112, or a single slot 114 may be occupied by portions of multiple windings 112. Further still, the windings 112 may occupy any portion (e.g., all, substantially all, half, etc.) of the volume of a slot 114, as is desired in the given application.

The stacked laminations 110 also define end teeth 110 c and 110 d extending from the base portion 110 a. As discussed above, it is known that the end tooth design of a linear motor can have an effect on the cogging of the linear motor.

According to an exemplary embodiment of the present invention, an end profile of each of the end teeth includes a first surface and a second surface. The first surface and the second surface are separated by a step which is substantially perpendicular to a plane defined by a plurality of permanent magnets of the linear motor. Referring to the exemplary embodiment of the present invention illustrated in FIG. 1, end teeth 110 c and 110 d are each provided with such a step separating respective first and second surfaces, as will be described in greater detail with respect to FIG. 3A.

FIG. 2 is a cross-sectional view of linear motor 200 in accordance with another exemplary embodiment of the present invention. Linear motor 200 includes magnet track 201 and coil assembly 208. Magnet track 201 includes support plate 202 (e.g., a steel plate) and a plurality of permanent magnets 204 disposed on support plate 202. For example, permanent magnets 204 may be glued or otherwise secured to support plate 202 at a predetermined spacing as is known to those skilled in the art. For purposes of describing certain exemplary features of the present invention, plane 206, which is substantially parallel to a top surface of permanent magnets 204, is shown in FIG. 2.

Coil assembly 208 includes a plurality of laminations 210 and a plurality of windings 212. Laminations 210 are stacked as is known to those skilled in the art, for example, to form an armature or the like. Stacked laminations 210 define base portion 210 a and a plurality of teeth 210 b extending from the base portion 210 a. Slots 214 are defined between adjacent teeth 210 b; between end tooth 210 c and an adjacent tooth 210 b; and between end tooth 210 d and an adjacent end tooth 210 b. In the exemplary embodiment of the present invention illustrated in FIG. 2, there are no flanged portions defined at an end of each of teeth 210 b (as in the exemplary embodiment illustrated in FIG. 1), and as such, the width of slot 214 is substantially the same along the length of teeth 210 b extending back towards base portion 210 a.

Windings 212 are provided in slots 214. For example, windings 212 may occupy each slot 214, or certain slots 214 may include windings 212 while others remain empty. Further, a single slot 214 may be occupied by a single winding 212, or a single slot 214 may be occupied by portions of multiple windings 212. Further still, the windings 212 may occupy any portion (e.g., all, substantially all, half, etc.) of the volume of a slot 214, as is desired in the given application.

The stacked laminations 210 also define end teeth 210 c and 210 d extending from the base portion 210 a. As discussed above, it is known that the end tooth design of a linear motor can have an effect on the cogging of the linear motor.

Referring to the exemplary embodiment of the present invention illustrated in FIG. 2, end teeth 210 c and 210 d are each provided with such a step separating respective first and second surfaces, as will be described in greater detail with respect to FIG. 3B.

FIG. 3A is a partial view of end tooth 110 c from linear motor 100 illustrated in FIG. 1 (and labeled as “A” in FIG. 1). While a detailed view of end tooth 110 d is not provided in FIG. 3A, it may be considered as a mirror image of end tooth 100 c (as shown in FIG. 1). Referring again now to FIG. 3A, the end profile of end tooth 110 c includes first surface 110 f and second surface 110 g separated by step 110 i. As illustrated by viewing FIGS. 1 and 3A in the aggregate, step 110 i is substantially perpendicular to plane 106. First surface 110 f is substantially parallel to plane 106, and second surface 110 g is configured at an acute angle “A” with respect to step 110 i. According to a preferred embodiment of the present invention, the acute angle “A” between second surface 110 g and step 110 i is between 60-90 degrees.

If first surface 110 f is considered to be at the top of lamination 110 (such that base portion 110 a is considered to be at the bottom of lamination 110), and if second surface 110 g is considered to be below first surface 110 f, then step 110 i is a step downward. All of the exemplary steps illustrated in the present application (i.e., steps 110 i, 210 i, 310 i, 410 i, 510 i, and 610 i) are shown in this manner. While such an arrangement is preferred, the present invention also contemplates the alternative, that is, a step upward from first surface 110 f to second surface 110 g.

Contiguous with first surface 110 f is flanged portion 110 h, as the end portions of plurality of teeth 110 b of linear motor 100 (illustrated in FIG. 1) include flanged portions 110 e. Consequently, end tooth 110 c (and end tooth 110 d, while not illustrated except in FIG. 1) include a flanged portion (i.e., flanged portion 110 h for end tooth 110 c).

Also shown in FIG. 3A are widths “W1” and “W2,” and height “H.” As shown in FIG. 3A, width W1 is the width of the portion of end tooth 110 c adjacent second surface 110 g (i.e., width W1 is parallel to plane 106, so width W1 is not the same as the length of second surface 110 g in FIG. 3A). Width W2 is the total width of the end tooth 110 c (excluding the added width of flanged portion 110 h in embodiments with such a flanged portion). Height H is the height of step 110 i. The inventors have determined that certain ratios of W1 to W2, and of H to W1 provide particularly desirable benefits in terms of togging reduction. For example, according to an exemplary embodiment of the present invention the ratio of W1/W2 is between 0.4-0.7, with a specific example being a ratio of W1/W2 of 0.6. For example, according to an exemplary embodiment of the present invention the ratio of H/W1 is between 0.3-0.5, with a specific example being a ration of H/W1 of 0.4.

FIG. 3B is a partial view of end tooth 210 c from linear motor 200 illustrated in FIG. 2 (and labeled as “B” in FIG. 2). As shown in FIG. 3B, the end profile of end tooth 210 c includes first surface 210 f and second surface 210 g separated by step 210 i. As illustrated by viewing FIGS. 2 and 3B in the aggregate, step 210 i is substantially perpendicular to plane 206. First surface 210 f is substantially parallel to plane 206, and second surface 210 g is configured at an acute angle “A” with respect to step 210 i. According to a preferred embodiment of the present invention, the acute angle “A” between second surface 210 g and step 210 i is between 60-90 degrees.

In contrast to end teeth 110 c and 110 d in FIG. 1, end teeth 210 c and 210 d in FIG. 2 do not include a flanged portion (e.g., flanged portion 110 h of end tooth 110 c).

Similarly to FIG. 3A, FIG. 3B also illustrates widths “W1” and “W2,” and height “H.” For example, according to an exemplary embodiment of the present invention the ratio of W1/W2 is between 0.4-0.7, with a specific example being a ratio of W1/W2 of 0.6. For example, according to an exemplary embodiment of the present invention the ratio of H/W1 is between 0.3-0.5, with a specific example being a ratio of H/W1 of 0.4.

FIGS. 4A, 4B, 5A, and 5B are additional examples of end tooth profiles according to exemplary embodiments of the present invention where each exemplary profile includes a step between a first surface and a second surface of the end profile of the end tooth. While each of these exemplary figures shows a portion of only a single end tooth, it is understood that two such end teeth may be provided, for example, as illustrated in FIGS. 1-2 (i.e., where the end teeth are mirror images of one another).

FIG. 4A is a partial view of end tooth 310 c configured for use in a linear motor such as that illustrated in FIGS. 1-2. As shown in FIG. 4A, the end profile of end tooth 310 c includes first surface 310 f and second surface 310 g separated by step 310 i. Step 310 i is substantially perpendicular to a plane defined by a plurality of permanent magnets (e.g., a plane similar to planes 106/206 shown in FIGS. 1-2). Each of first surface 310 f and second surface 310 g is substantially parallel to the plane defined by the plurality of permanent magnets, and as such, an angle “A” defined between second surface 310 g and step 310 i is approximately 90 degrees. Similar to end tooth 110 c illustrated in FIG. 3A, end tooth 310 c includes flanged portion 310 h.

FIG. 4B is a partial view of end tooth 410 c configured for use in a linear motor such as that illustrated in FIGS. 1-2. As shown in FIG. 4B, the end profile of end tooth 410 c includes first surface 410 f and second surface 410 g separated by step 410 i. Step 410 i is substantially perpendicular to a plane defined by a plurality of permanent magnets (e.g., a plane similar to planes 106/206 shown in FIGS. 1-2). Each of first surface 410 f and second surface 410 g is substantially parallel to the plane defined by the plurality of permanent magnets, and as such, an angle “A” defined between second surface 410 g and step 410 i is approximately 90 degrees. Similar to end tooth 210 c illustrated in FIG. 3B, end tooth 410 c does not include a flanged portion (e.g., such as flanged portion 110 h of end tooth 110 c).

FIG. 5A is a partial view of end tooth 510 c configured for use in a linear motor such as that illustrated in FIGS. 1-2. As shown in FIG. 5A, the end profile of end tooth 510 c includes first surface 510 f and second surface 510 g separated by step 510 i. Step 510 i is substantially perpendicular to a plane defined by a plurality of permanent magnets (e.g., a plane similar to planes 106/206 shown in FIGS. 1-2). First surface 510 f is substantially parallel to the plane defined by the plurality of permanent magnets. Second surface 510 g is configured at an obtuse angle “A” with respect to step 510 i. According to a preferred embodiment of the present invention, the obtuse angle “A” between second surface 510 g and step 510 i is between 90-120 degrees. Similar to end tooth 110 c illustrated in FIG. 3A, end tooth 510 c includes flanged portion 510 h.

FIG. 5B is a partial view of end tooth 610 c configured for use in a linear motor such as that illustrated in FIGS. 1-2. As shown in FIG. 5B, the end profile of end tooth 610 c includes first surface 610 f and second surface 610 g separated by step 610 i. Step 610 i is substantially perpendicular to a plane defined by a plurality of permanent magnets (e.g., a plane similar to planes 106/206 shown in FIGS. 1-2). First surface 610 f is substantially parallel to the plane defined by the plurality of permanent magnets Second surface 610 g is configured at an obtuse angle “A” with respect to step 610 i. According to a preferred embodiment of the present invention, the obtuse angle “A” between second surface 610 g and step 610 i is between 90-120 degrees. Similar to end tooth 210 c illustrated in FIG. 3B, end tooth 610 c does not include a flanged portion (e.g., such as flanged portion 110 h of end tooth 110 c).

Each of end teeth 310 c, 410 c, 510 c, and 610 c (respectively illustrated in FIGS. 4A, 4B, 5A, and 5B) defines widths “W1” and “W2,” and height “H.” As with end teeth 110 c and 210 c described above, according to an exemplary embodiment of the present invention the ratio of W1/W2 for each of end teeth 310 c, 410 c, 510 c, and 610 c is between 0.4-0.7, with a specific example being a ratio of W1/W2 of 0.6. Likewise, according to an exemplary embodiment of the present invention the ratio of H/W1 for each of end teeth 310 c, 410 c, 510 c, and 610 c is between 0.3-0.5, with a specific example being a ratio of H/W1 of 0.4.

It is noteworthy that, in contrast to the width W1 in FIGS. 3A-3B and FIGS. 5A-5B, width W1 in FIGS. 4A-4B is the same as the length of the second surface (i.e., second surface 310 g in FIG. 4A, second surface 410 g in FIG. 4B).

Referring again to exemplary linear motors 100 and 200 shown in FIGS. 1-2 (wherein such linear motor may utilize any end tooth within the scope of the present invention, including those shown in FIGS. 3A-3B, 4A-4B, and 5A-5B), either of the magnet track and the coil assembly may be the fixed member of the linear motor (i.e., a stator), while the other of the magnet track and the coil assembly may be the moving member of the linear motor.

As is known to those skilled in the art, a number of features of a linear motor may be optimized to achieve a desired result such as cogging reduction. For example, such features may include: (1) a spacing or pitch of the permanent magnets included in the magnet track; (2) the spacing or pitch of the plurality of teeth of the coil assembly; (3) the width of the slots between the teeth; (4) the length of the teeth, amongst other features. These features may be optimized independently, or in conjunction with one another, to achieve a desired result (e.g., cogging reduction through phase shifting).

The linear motor of the present invention may find application in a number of technical fields. One exemplary area of use is with a wire bonding machine, wherein a linear motor according to the present invention may be used to provide linear motion along the x-axis or the y-axis, or both. More specifically, for example, such linear motors may be used to provide linear motion to a bond head assembly of a wire bonding machine along the x-axis of the bond head assembly, the y-axis of the bond head assembly, or both. Of course, the linear motor of the present invention will find use in any of a number of other technical fields where a reduction in cogging is desired.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 

1. A linear motor comprising: a magnet track including a plurality of permanent magnets; and a coil assembly including a plurality of laminations, the coil assembly defining a plurality of teeth having slots therebetween, the plurality of teeth including (1) two end teeth and (2) at least one non-end tooth arranged between the two end teeth, each of the two end teeth defining an end profile including a first surface and a second surface, the first surface and the second surface being separated by a step which is substantially perpendicular to a plane defined by the plurality of magnets, the coil assembly also including a plurality of coils at least partially disposed in at least a portion of the slots defined by the plurality of teeth.
 2. The linear motor of claim 1 wherein the first surface is substantially parallel to the plane defined by the plurality of magnets.
 3. The linear motor of claim 1 wherein the second surface is substantially parallel to the plane defined by the plurality of magnets.
 4. The linear motor of claim 1 wherein each of the first surface and the second surface is substantially parallel to the plane defined by the plurality of magnets.
 5. The linear motor of claim 4 where the first surface is closer to the at least one non-end tooth than the second surface.
 6. The linear motor of claim 5 wherein a ratio of (1) a height of the step to (2) a width of the second surface is between 0.3-0.5.
 7. The linear motor of claim 5 wherein a ratio of (1) a width of the second surface to (2) a width of the end tooth is between 0.4-0.7.
 8. The linear motor of claim 5 wherein the step is a downward step if the first surface is considered to be the top of the plurality of laminations and the second surface is beneath the first surface.
 9. The linear motor of claim 1 where the first surface is closer to the at least one non-end tooth than the second surface.
 10. The linear motor of claim 9 wherein a ratio of (1) a height of the step, to (2) a width of a portion of the end tooth adjacent the second surface is between 0.3-0.5, the width of the portion of the end tooth adjacent the second surface being parallel to the plane defined by the plurality of magnets.
 11. The linear motor of claim 9 wherein a ratio of (1) a width of a portion of the end tooth adjacent the second surface, to (2) a width of the end tooth is between 0.4-0.7, the width of the portion of the end tooth adjacent the second surface being parallel to the plane defined by the plurality of magnets.
 12. The linear motor of claim 9 wherein the step is a downward step if the first surface is considered to be the top of the plurality of laminations and the second surface is beneath the first surface.
 13. The linear motor of claim 9 wherein the second surface is configured at an acute angle with respect to the step.
 14. The linear motor of claim 13 wherein the second surface is configured at an angle between 60-90 degrees with respect to the step.
 15. The linear motor of claim 9 wherein the second surface is configured at an obtuse angle with respect to the step.
 16. The linear motor of claim 15 wherein the second surface is configured at an angle between 90-120 degrees with respect to the step.
 17. The linear motor of claim 1 wherein the at least one non-end tooth includes a flanged portion at an end thereof, the flanged portion being wider than the remainder of the at least one non-end tooth.
 18. The linear motor of claim 1 wherein the at least one non-end tooth has a substantially constant width along its entire length. 